Radiation source and means for starting



March 3, 1959 F. B. HUTCHINSON RADIATION SOURCE AND MEANS FOR STARTINGFiled Aug. 28, 1953 INVENTOR.

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ATTORNEYS" RADIATION SOURCE AND MEANS FQR STARTKNG 7 Franklin B.Hutchinson, Fair-field, Conn, assignor to The Perkin-Elmer Corporation,Norwalk, Conn, a New York corporation Application August 28, 1953,Serial No. 377,097 12 Claims. (Cl. 250--85) This invention relates tosources of radiant energy for use in such instruments as spectrometers,gas analyzers, etc., and is concerned more particularly with a noveldevice for producing radiation, which includes a glower of the Nernsttype and means for bringing the glower rapidly to operating condition.

At the present time, infrared spectrometers require a source of radiantenergy which is especially strong in the range from two to fifteenmicrons and up, and one source of such radiation, which is in commonuse, is the silicon carbide rod sold commercially under the trade nameGlobar. While such a rod is satisfactory in most respects, it mustfrequently be of such size as to require water cooling and the provisionof such cooling means is sometimes inconvenient. A second source ofinfrared radiation in general use is the Nernst glower, which is a bodycomposed of rare earth oxides and can be operated without cooling meansat temperatures higher than may be reached with rod sources. However,the glower has a negative temperature coeflicient of resistance and itis essentially non-conductive at room temperature with its resistancedecreasing as its temperature is raised. Because of this characteristic,a glower requires for its functioning an external source of heat toraise its temperature and thereby lower its resistance, until it becomesconductive and is in operating condition. The heating of the glower toplace it in condition for use requires time, particularly if theconstruction of the instrument is such that heat can be applied at oneside only of the glower, and the loss of instrument time resulting fromthe requirement that the glower be externally heated before use is anobjection to the glower. I

" The present invention is directed to the provision of a novel devicefor producing radiation, which contains a glower but requires less timethan prior glower sources for bringing the glower to operatingcondition. The new device includes a main source of voltage, a heater so2,876,361 Patented Mar. 3, 1959 "too when the heater is functioning. Thesubsidiary source of voltage is the secondary winding 15 of atransformer 16 and the heater is connected across the winding terminalsand the connections include means for reducing the magnitude of thesubsidiary voltage. Any suitable expedient may be employed for thepurpose, as, for example, the connections may include an adjustableresistor, which can be adjusted to increase its resistance and effect acorresponding reduction in the subsidiary voltage applied to the heater,or the connections may inelude a switch, which can be opened to causethe subsidiary voltage impressed on the heater to be reduced to zero.The means for reducing the subsidiary voltage is automatically operatedand, in the circuit illustrated, the reducing means is the switch 17,which is mechanically connected to the adjusting element of the variableresistor 12 and is opened through that mechanical connection as soon asthe element is moved to increase the resistance of resistor 12 above aselected value. The primary winding 18 of the transformer is energizedfrom any suitable source and, in the instrument shown, is conne'ctedacross the terminals in and i1.

A detector responsive to radiation and illustrated as a phototube i9 isdisposed adjacent the glower in position to receive radiation therefromand the output of the detector is fed into a conventional differentialamplifier 20, where it is compared with a reference voltage derived fromany suitable source, such as a potentiome ter 21 receiving current froma source 22. Any excess of the output of the detector over the referencevoltage is amplified and fed to an actuator 23 operating the movableelement of resistor 12. T he combination of the variplaced as to heatthe glower, and a subsidiary source of voltage, which can be impressedupon the heater. The

main and subsidiary sources of voltage can be connected in series aidingand the sum of the voltages can be impressed upon the glower, so thatthe glower will become conductive at a lower temperature and a shorterheating time will be required to bring the glower to that temperature.After the glower has become conductive, the magnitude of the subsidiarysource of voltage is automatically reduced and the subsidiary sourceremains in this condition, until used again in starting the glower.

For a better understanding of the invention, reference may be made tothe accompanying drawing, the single figure of which is a circuitdiagram of the new device.

' The form of the device illustrated in the drawing comprises terminalsIll, 11, to which an A. C. line voltage may be applied. The terminal 10is connected through able resistor and its actuator may take variousforms, and the resistor may be of the carbon pile type and actuated by asolenoid. Another suitable actuator is that shown in Cohen Patent2,550,779, issued May 11, 1951.

In the operation of the device illustrated, A. C. line voltage appliedto the terminals it andll appears across the primary winding 18 oftransformer 16 and the closing of switch 17 causes the voltage developedacross the secondary winding 15 of the transformer to operate heater 14.Witha line voltage of 117 volts, for example, the secondary voltage maybe 20 volts. The heater and the transformer secondary winding are soconnected to the glower that the line voltage and the voltage developedacross the secondary winding of the transformer are in series aidingrelation with the result that the voltage across the glower when it isvirtually non-conductive is the sum of the two voltages and, in theexample given, is equal to 137 volts. Since a voltage greater than linevoltage is impressed upon the glower in its non-conductive state, itbecomes self-conductive at a lower temperature than would be required ifline voltage only were impressed upon it.

When the temperature of the glower has been increased sufiiciently topermit it to pass enough current toraise its temperature further with anaccompanying lowering of its resistance, the glower emits radiation,which falls upon the detector 19. So long as the output of the detectoris below the reference voltage, the secondary winding of the transformeris connected to heater l4 and the sum of the line and the transformersecondary voltages is impressed upon the glower. As soon as thephototube output exceeds the reference voltage, the amplified differencein voltages, or error signal, causes the resistor actuator to operatethe resistor 12 to increase its resistance from its minimum value. Themovement of the adjustable element of the resistor then opens switch 17,so that thereafter the body and heater have line voltage only impressedthereon. Under these conditions very little voltage drop is developedacross the heater because it has much less impedance value than theglower. Conse-v quently, nearly all the line voltage is impressed uponthe glower. During the operation of the device, the phototube actsthrough the means described to regulate resistor 12 and keep the outputof radiation from the glower; 13 within selected limits.

It will be apparent to those skilled in the art that the amount ofradiation which will actuate the device to remove the subsidiary voltagefrom the heater and the glower, is determined by the adjustment of thevariable reference signal. The setting of the variable tap onpotentiometer 21 therefore may be used to effectively control the amountof emitted radiation from glower 13 which will render the heatersubstantially inoperative and simultaneously reduce the voltage acrossthe glower 13.

In the infrared spectroscopy art it is most desirable to be able tocontrol and adjust this operative point from outside the instrumentwithout risking any interference with the radiation source itself. Thepresent invention embodies this most desirable feature in addition tothe novel arrangement by which several of the components of thecombination perform dual and simultaneous functions.

I claim:

1. In a device for producing radiation, the combination of a body ofmaterial capable of emitting radiation in response to the flow ofelectrical current therethrough and having a negative temperaturecoefficient of resistance, a main source of voltage connected in circuitwith said body, a heater serially connected between said main source ofvoltage and said body and positioned to raise the temperature of saidbody, a subsidiary source of voltage, means for impressing saidsubsidiary voltage across said heater and in series aiding relation tosaid main voltage, and radiation-sensitive means for controlling theflow of current through said body including means for disconnecting saidsubsidiary voltage in response to a determinable amplitude of radiationby said body.

2. In a device for producing radiation, the combination of a body ofmaterial capable of emitting radiation in response to the flow ofelectrical current therethrough and having a negative temperaturecoefficient of resist.- ance, a main source of voltage connected incircuit with said body, a heater serially connected between said mainsource of voltage and said body and positioned to raise the temperatureof said body, a subsidiary source of voltage, means for impressing saidsubsidiary voltage across said heater and in series aiding relation tosaid main voltage, and adjustable current controlling means responsiveto the radiation of said body for regulating the flow of currenttherethrough, including means for disconnecting said subsidiary voltageafter a determinable radiation output of said body. 3. In a device forproducing radiation, the combination of a body of material capable ofemitting radiation in response to the flow of electrical currenttherethrough and having a negative temperature coefficient ofresistance, a main source of voltage connected in circuit with saidbody, a heater serially connected between said main source of voltageand said body and positioned to raise the temperature of said body, asubsidiary source of voltage, means for impressing said subsidiaryvoltage across said heater and in series aiding relation to said mainvoltage, and adjustable current controlling means responsive to theradiation of said body for regulating the flow of current therethrough,including means for disconnecting said subsidiary voltage after adeterminable amplitude of said current flow.

4. In a device for producing radiation, the combination of a body ofmaterial capable of emitting radiation in response to the flow ofelectrical current therethrough and having a negative temperaturecoefiicient of resistance, a main source of voltage connected in circuitwith said body, a heater serially connected between said main'soui'ce'of voltage and said body and positioned to raise thetemperature of said body,'means for deriving a sub sidiary voltage fromsaid main source of voltage, means for impressing said subsidiaryvoltage across said heater and in series aiding relation to said mainvoltage, and radiation-sensitive means for controlling the flow ofcurrent through said body including means for disconnecting saidsubsidiary voltage in response to a determinable amplitude of radiationby said body.

5. In a device for producing radiation, the combination of a body ofmaterial capable of emitting radiation in response to the flow ofelectrical current therethrough and having a negative temperaturecoefficient of resistance, a main source of voltage connected in circuitwith said body, a heater serially connected between said main source ofvoltage and said body and positioned to raise the temperature of saidbody, a subsidiary source of voltage, means for impressing saidsubsidiary voltage across said heater and in series aiding relation tosaid main voltage, and means responsive to the radiation of said bodyfor producing a signal as a function of the intensity thereof, a sourceof reference signal, means connected to receive said radiation intensitysignal and said reference signal for producing an output signal as afunction of the difference therebetween, and means responsive to adeterminable output signal for disconnecting said subsidiary voltage.

6. In a device for producing radiation, the combination of a body ofmaterial capable of emitting radiation in response to the flow ofelectrical current therethrough and having a negative temperaturecoefficient of resistance, a main source of voltage connected in circuitwith said body, a heater serially connected between said main source ofvoltage and said body and positioned to raise the temperature of saidbody, a subsidiary source of voltage, means for impressing saidsubsidiary voltage across said heater and in series aiding relation tosaid main voltage, and means responsive to the radiation of said bodyfor producing a signal as a function of the intensity thereof, a sourceof reference signal, means connected to receive said radiation intensitysignal and said reference signal for producing an output signal as afunction of the difference therebetween, and means for continuouslyregulating the current flow through said body in accordance with theamplitude of said difference signal, including means for disconnectingsaid subsidiary voltage in response to a determinable amplitude of saiddifference signal.

7. In a device for producing radiation, the combination of a body ofmaterial capable of emitting radiation in response to the flow ofelectrical current therethrough and having a negative temperaturecoefficient of resistance, a main source of voltage connected in circuitwith said body, a heater serially connected between said main source ofvoltage and said body and positioned to raise the temperature of saidbody, a transformer having its primary winding connected across saidmain source of voltage and its secondary winding connected to saidheater for impressing a subsidiary voltage thereacross in series aidingrelation with said main voltage, radiation-sensitive means forcontrolling the flow of current through said body including means fordisconnecting said subsidiary voltage in response to a determinableamplitude of radiation by said body.

8. In a device for producing radiation, the combination of a body ofmaterial capable of emitting radiation in response to the flow ofelectrical current therethrough and having a negative temperaturecoefficient of resistance, a main source of voltage connected in circuitwith said body, a heater serially connected between said main source ofvoltage and said body and positioned to raise the temperature of saidbody, a transformer having its primary-winding connected across saidmain source of voltage and its secondary winding connected to saidheater'for impressing asubsidiary voltage. thereacross in series aidingrelation with said main voltage, radiation- "s'ensitive means forcontrollingthe flow of current through said body including means fordisconnecting the secondary winding of said transformer from said heaterin response to a determinable amplitude of radiation by said body.

9. In a device for producing radiation, the combination of a body ofmaterial capable of emitting radiation in response to the flow ofelectrical current therethrough and having a negative temperaturecoefficient of resistance, a main source of voltage connected in circuitwith said body, a heater serially connected between said main source ofvoltage and said body and positioned to raise the temperature of saidbody, a subsidiary source of voltage, means for impressing saidsubsidiary voltage across said heater and in series aiding relation tosaid main voltage, and means responsive to the radiation of said bodyfor producing a signal as a function of the intensity thereof, a sourceof reference signal, means connected to receive said radiation intensitysignal and said reference signal for producing an output signal as afunction of the difierence therebetween, variable impedance meansconnected in circuit with said body and said main voltage source, meansto continuously vary the effective value of said impedance in accordancewith the amplitude of said difference signal, said last-named meansincluding means for disconnecting said subsidiary voltage from saidheater in response to a determinable amplitude of said differencesignal.

10. A device for producing radiation in accordance with claim 1 whereinthe means for disconnecting said subsidiary voltage comprises arelay-operated switch.

11. In a device for producing radiation, the combination of a body ofmaterial capable of emitting radiation in response to the fiow ofelectrical current therethrough and having a negative temperaturecoeificient of resistance, a main source of voltage connected in circuitwith said body and positioned to raise the temperature of said body, asubsidiary source of voltage derived from said main source of voltage,means for impressing said subsidiary voltage across the heater and inseries aiding relation with said main voltage, whereby an increasedamplitude of voltage is impressed upon said body when it issubstantially non-conductive and said body is simultaneously heated to aconductive condition.

12. In a device for producing radiation, the combination of a body ofmaterial capable of emitting radiation in response to the flow ofelectrical current therethrough and having a negative temperaturecoefiicient of resistance, a main source of voltage connected in circuitwith said body, a heater serially connected between said main source ofvoltage and said body and positioned to raise the temperature of saidbody, a subsidiary source of voltage, means for impressing saidsubsidiary voltage across said heater and in series aiding relation tosaid main voltage, and means responsive to the radiation of said bodyfor producing a signal as a function of the intensity thereof, anadjustable reference signal, means connected to receive said radiationintensity signal and said reference signal for producing an outputsignal as a function of the difference therebetween, variable impedancemeans connected in circuit with said body and said main voltage source,means to continuously vary the effective value of said impedance inaccordance with the amplitude of said diiference signal, said last-namedmeans including means for disconnecting said subsidiary voltage fromsaid difference signal dependent upon the adjustment of said referencesignal.

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